Electronic components for providing the required power are part of such power modules. For example, in connection with electric motors the power is typically in the kilowatt range. Power modules are used for providing control signals and/or for the evaluation of measured signals. As a rule, the active and passive components of the circuit arrangement of such power module require a construction that has a low inductance to avoid excess voltages. Active components include, for example, power components that are working in a switching operation at high speed current changes, particularly integrated switching circuits operating as power switches. Passive components include, for example resistors, for example shunts for current measuring, and capacitors. Thus, the circuit arrangement of the power module is customarily applied on an insulating carrier body or an insulating substrate consisting as a rule of a ceramic material. For mechanical stabilization and for heat dissipation of the dissipation power of the components of the circuit arrangement, particularly the power components, the carrier body is secured to a massive metallic cooling body, for example a copper or an aluminum plate. The carrier body is secured to the cooling body by a bonding layer, for example by means of solder or a heat conducting paste to form a thermal connection. The insulation or potential separation between the electronic components of the circuit arrangement and the cooling body is realized through the insulating carrier body.
The substrate or the carrier body and the cooling body have different thermal expansion coefficients since the former is made of ceramic material and the latter is made of metal. Therefore, the substrate and the cooling body have different thermal expansions. As a result, on the one hand, a relatively thick bonding layer is required between the carrier body and the cooling body, particularly in connection with a carrier body having a large surface for equalizing tensions. The thick bonding layer causes a high heat resistance particularly due to inclusions in the bonding layer such as shrink holes in a solder layer, which negatively influence the heat conductivity. Thus, a poor heat transition exists between the electronic components of the circuit arrangement and the cooling body due to the heat resistances that are formed by the inclusions. As a result, the dissipation of the dissipation power of the electronic components becomes difficult. On the other hand, the connection between the carrier body and the cooling body is frequently impaired, whereby the life duration and thus the reliability of the power modules is significantly reduced. This is particularly true where the power module must work in a large temperature range and under the temperature changes that such a large range entails.